Steve: the size of the ESL panel has no impact on its upper frequency response. Six inches square or one inch square will extend to the same frequency if they have the same diaphragm material. The narrow line source strip will provide wide dispersion of high frequencies. As SY mentioned there will be interaction between the panel sections in the horizontal plane. I don't imagine this will be any worse than with the 5 or 6 degree angle between vertical panels in a 2+2 Acoustat for example. But I think that when you compare a 2+2 Acoustat to a 0ne plus 0ne Acoustat the difference in stage and image is likely as a result of the interaction of the two vertical panels in the 2+2. The 0ne plus 0ne provides better stage and image at the cost of overall output and bass level. Best regards Moray James.

Thanks Andy, can you tell me does the Spectra 66/6600 sound different from the other Acoustat models, especially in the treble response? I thought I read somewhere they might use a smaller (less wide) treble strip for a stronger more extended treble response?

This is exactly what the ER Audio ESL-3 that I posted above has, it is a two way design with a dedicated 2" wide central treble strip that is capable of doing 25 kHz. When you hear it, it makes other stats like Martin Logan and my brother's Acoustat Model 1 sound a little lacking in treble attack.

Regards,

Steve.

All Spectra models, regardless of size, use the same 1/2-panel width for the full range sector (i.e. the only area playing high frequencies). Therefore, I think the sound of all the Spectra models is very similar, with only bass extension and dynamics increasing in the larger models. In this way, the Spectra series solved the compromises inherent in the older models - that is, narrower models tended to have the best imaging but limited bass capabilities, whereas the wider models had better bass response but inferior imaging. With the Spectra series, the same character of sound is available across the model line, with merely more of it as the size and price goes up. Perhaps you can tell I'm pretty proud of what we accomplished in the Spectra series - I am!

When I left Rockford, I was using Spectra 1100's, and a few years later when I switched to 4400's, I felt that I lost NONE of the imaging qualities of the smaller speaker. The only changes were positive - more impact and bass extension. So, if you like what you hear in one of the smaller models, I feel confident that you will also like any of the larger models.

All Spectra models, regardless of size, use the same 1/2-panel width for the full range sector (i.e. the only area playing high frequencies). Therefore, I think the sound of all the Spectra models is very similar, with only bass extension and dynamics increasing in the larger models. In this way, the Spectra series solved the compromises inherent in the older models - that is, narrower models tended to have the best imaging but limited bass capabilities, whereas the wider models had better bass response but inferior imaging. With the Spectra series, the same character of sound is available across the model line, with merely more of it as the size and price goes up. Perhaps you can tell I'm pretty proud of what we accomplished in the Spectra series - I am!

Nice to see drawings I made some years ago surfacing in different places. Note the drawing also shows the panel wiring color-codes, which helps to decipher the mess of wiring inside the speakers. This drawing was originally posted on the AudioCircuit, in response to similar questions.

When developing the larger Spectra models(3 panels wide) did you experiment with the horizontal placement of the 1/2 panel portion playing full range? (inside placement .vs. centered .vs. outside)

No, we did not. The resistors feeding the mids/lows and lows-only sectors create a time delay (as do all R-C filters), which effectively creates the curved dispersion: electrically curved instead of mechanically curved. Therefore, it makes sense that the full range sector is close to the the inner edge of each speaker, so that adjacent sectors are time-delayed (or curved away from the listener) for a smooth dispersion pattern.

If you didn't know, Spectra is an acronym for Symmetric Pair Electrically Curved TRansducer.

This is not to say that other arrangements of the sectors would not yield acceptable results, to some ears, but I think the factory arrangements do make for the best imaging/sound stage in the widest variety of rooms.

No, we did not. The resistors feeding the mids/lows and lows-only sectors create a time delay (as do all R-C filters), which effectively creates the curved dispersion: electrically curved instead of mechanically curved. Therefore, it makes sense that the full range sector is close to the the inner edge of each speaker, so that adjacent sectors are time-delayed (or curved away from the listener) for a smooth dispersion pattern.

If you didn't know, Spectra is an acronym for Symmetric Pair Electrically Curved TRansducer.

This is not to say that other arrangements of the sectors would not yield acceptable results, to some ears, but I think the factory arrangements do make for the best imaging/sound stage in the widest variety of rooms.

Thanks for the info and the nicely drawn Spectra hookup diaphragm.

The reason I had asked about the placement of the full range section in the larger Spectra models is that I have been experimenting with my own wire ESLs. In general I found the sweet spot to be larger and imaging more stable when the full range section was placed in the center and the ladder resistor networks worked outwards toward the inner and outer edges of the panel. However, my panels are not nearly as wide as the Spectra 6600 so perhaps keeping the full range section away from the side walls with the large Spectra panels is more advantageous.

My friend has a pair of 2+2's (I think). They have been in storage for a very long time (maybe 15 years). At some point he may ask me to check them out and start them up. What is the safe and sane procedure?